The present invention relates to transmit and receiving antenna diversity in wireless networks, in particular in wireless networks with direct mode, i.e. the possibility that network devices, e.g. mobile terminals, directly communicate with each other without using a central station or access point as repeater.
An exemplary wireless network is shown in FIG. 3. Generally, mobile terminals in wireless networks, such as the IEEE 1394 based HIPERLAN type 2 network which is developed under supervision of ETSI comprise several different directed antennas to be able to perform a receiving antenna diversity in regard to the central controller or access point 18. In this case the receiver of a mobile terminal 1, 15, 16, 17 determines the best receiving antenna during a downlink period of a communication with the central controller or access point 18 and the transmitter of said mobile terminal uses the same antenna during an uplink period. An IEEE 1394 bus with connected network devices is exemplary shown only for the fourth mobile terminal 17.
The state of the art on both transmit and receiving antenna diversity in wireless networks with direct mode is performed by switching between all transmit and receiving antennas in order to assess the provided radio link quality in all possible cases. In case a first mobile terminal having a medium access control identifier, i.e. MAC-ID, MT1 comprises N directed transmit and receiving antennas and a second mobile terminal having medium access control identifier MT2 comprises M directed transmit and receiving antennas there is the need to perform Nxc2x7M measurements until the best antenna pair is identified, since for each of the N directed transmit antennas of the first mobile terminal with MAC-ID MT1 all M receiving antennas of the second mobile terminal with MAC-ID MT2 have to be switched through to determine the antenna pair having the best performance. These Nxc2x7M measurements need a rather long time when considering systems with a bigger number of transmitting and receiving antennas, e.g. 8 antennas per mobile terminal.
Therefore, it is the object of the present invention to reduce the time to identify the best antenna pair in case of transmit and receiving antenna diversity.
This object is solved with a method to perform a transmit and receiving antenna diversity in-between a first network device and a second network device of a wireless network according to independent claim 1, a network device within a wireless network which is comprising a number of directional antennas according to independent claim 4 and an antenna calibration signal according to independent claim 11. Preferred embodiments thereof are respectively defined in the dependent subclaims.
According to the present invention a network device of a wireless network, such as a mobile terminal of an IEEE1394 based HIPERLAN type 2 network, which comprises a number of directional antennas to perform antenna diversity additionally comprises an omni-directional antenna.
Therewith, to perform a transmit and receiving antenna diversity in-between first and second of such network devices according to the present invention the following steps are performed:
using the omni-directional antenna of the first network device to transmit a calibration signal from the first network device to the second network device;
identifying the best receiving antenna of the second network device by successively switching all directional antennas and the omni-directional antenna of the second network device into its receiving path and respectively measuring the received signal quality, and setting said identified best receiving antenna as transmit and receiving antenna of said second network device;
using the set transmit and receiving antenna of said second network device to transmit a calibration signal from the second network device to the first network device; and
identifying the best receiving antenna of the first network device by successively switching all directional antennas and the omni-directional antenna of the first network device into its receiving path and respectively measuring the received signal quality, and setting said identified best receiving antenna as transmit and receiving antenna of said first network device.
Therewith, according to the present invention the amount of measurements needed to be performed until the best antenna pair is identified is reduced to N+M+2 in case the first network device comprises N directional antennas and 1 omni-directional antenna and the second network device comprises M directional antennas and 1 omni-directional antenna.
Said omni-directional antenna of a network device according to the present invention is preferably separate from the directional antennas, but according to a further preferred embodiment of the present invention it is also possible that said omni-directional antenna is built by a parallel connection of several or all of said directional antennas.
This further preferred embodiment according to the present invention has the advantage that existing network devices can easily be adapted to the inventive method without considerable changes in hardware, but by mainly providing the new control method for antenna diversity according to the present invention.
An antenna calibration signal that is to be used in the inventive method to perform a transmit and receiving antenna diversity with a network device according to the present invention is characterized in that a signal is used which is already available within the mobile terminal.
Therefore, no additional memory space is needed to store the calibration signal according to the present invention.
Preferably one or more B16 quarter symbols are used to compose the antenna calibration signal, wherein a B16 is a quarter symbol within a BCCH/uplink preamble according to the IEEE1394 based HIPERLAN type 2 network.
The use of this signal inherits the advantage that the peak to average power ratio and dynamic range is low.
Of course, the calibration signal has to be transmitted during the whole time of switching through all available antennas of the respective receiving network device and it has to be homogeneous over its signal period.